Big banks prefer making multimillion-dollar loans to large corporations instead of small-businesses because the fee income is greater and it allows them to hire experts in industries that they want to target.
The poorest of the poor in the microfinance world pay back at rates as high as 99%. Wall Street banks not only did not pay back, they took from us and paid themselves bonuses. Guess they aren't very good bankers are they?
The banking industry mentality is deeply conservative -- not the kind that makes sure that loans are collateralized and deposits protected. Rather, it is a mentality produced by an out-of-date understanding of the world.